1. Field of Invention
The present invention relates to bearing defect detectors and in particular to an integrity test for an acoustic system for detecting defects in the bearings of moving railroad cars.
2. Description of the Prior Art
Heretofore, the detection of defects in railway car bearings has relied upon stationary infrared sensing means along railroad tracks to detect an abnormal heat rise associated with bearing failure in passing railroad cars. While such systems have enjoyed widespread use and an industry-wide reputation for reliability, they suffer from a serious drawback in that they detect a defect only after a damaging heat build-up has occurred within the bearing. Furthermore, this heat build-up often does not occur until a total bearing failure is imminent, thereby normally warranting an immediate stopping of the train so that an emergency field repair may be done. As this requires a delay in the train until a repair team may arrive with the necessary equipment, the total cost of this procedure can be very high.
From U.S. Pat. Nos. 4,790,190 and 4,843,885 along with pending patent application Ser. No. 367,890 filed July 6, 1989 it is known that defects in tapered roller bearings, such as those used in railroad cars, produce sounds during operation at characteristic frequencies dependent upon the location or type of defect (i.e., at the bearing cup, cone, or roller), the combination of the size of the wheel and the bearing capacity (frequently encountered combinations on railroads are a 28 inch wheel with a 70 ton capacity bearing, a 33 inch wheel with a 70 ton capacity bearing, and a 36 inch wheel with a 100 ton capacity bearing), and the speed of the train.
Additionally, irregularities in the wheel circumference ("flats") produce a characteristic frequency dependent upon wheel rotational frequency.
Thus for any given train speed, a defective bearing will produce a sound at a characteristic frequency dependent upon the location of the defect in the bearing and the combination of the train speed, wheel size and bearing capacity. Wheel flats will produce a sound at additional characteristic frequencies depending on train speed and wheel size.
Furthermore, it is known from the aforementioned references that the sounds emanating from a defective bearing are amplitude modulated on a carrier frequency in the 10-12 kilohertz range. Therefore, these references disclose a method and apparatus for on-line testing of bearing defects using amplitude demodulation to remove extraneous sounds from electronic analysis as the train passes the apparatus. This allows testing to be done at diverse, possibly isolated, locations throughout the railroad system notwithstanding inclement weather or other obstacles. While this apparatus and method has shown great utility, there is a need to be able to self-test the electronic apparatus automatically and efficiently. In some cases, the test may be monitored from a centralized location, unimpeded by weather conditions or the isolation of the apparatus. Furthermore, the test may be initiated at regular intervals or immediately before and/or after the passage of a train.